Greater Glasgow and Clyde Medicines

SNAP: A shorter regimen for the management of paracetamol overdose in adults

Key messages

  • Following a successful pilot period, the new SNAP (Scottish & Newcastle Acetylcysteine Protocol) guideline is being introduced across GGC, adult services, on 8th Feb 2021
  • The GGC-approved guideline is titled ‘Adult Paracetamol Overdose Protocol and Shortened N-acetylcysteine (NAC) Administration Chart’. Click here for full guideline
  • The guideline contains 5 management flowcharts to support prescribing (dependent on time of presentation and type of overdose)
  • The GGC Acetylcysteine Prescription Chart has been updated and will now be printed as a 10-page booklet (with the new guideline integrated); an initial supply is being organised for key clinical areas (click here for memo on StaffNet with full details)
  • A 9-minute educational video is available (click here) and the key clinical messages are outlined below

Advantages of the new SNAP guideline:
Paracetamol overdose has traditionally been managed using 300mg/kg acetylcysteine (N-acetylcysteine, NAC) administered intravenously over 21 hours using 3 infusions. Recently, the new SNAP regimen has been introduced across several sites in the UK and is included as a treatment option on TOXBASE. This regimen provides the same dose of NAC over a 12-hour period using 2 infusions and has 3 main advantages:

  1. It is simpler to use
  2. Is associated with fewer adverse drug reactions
  3. Shorter length of stay for most patients

Some patients may require more than 2 infusions of NAC; the new guideline provides guidance on how to manage this and the prescription chart has additional prescribing boxes to support safe prescribing.

Important clinical messages:

Important points regarding the management of paracetamol overdose and the use of the SNAP protocol (see video here for further information):

  • Acetylcysteine (N-acetylcysteine, NAC) is most efficacious when administered within 8 hours of paracetamol ingestion
  • For paracetamol overdose presenting ≤ 24 hours, total paracetamol ingestion (mg/kg) should be estimated on admission as this will guide the need for immediate treatment with NAC
  • Bloods (including a serum paracetamol level) should be taken 2 hours prior to the end of the second infusion in order to allow timely decision making with regards continuation or completion of NAC
  • NAC (& paracetamol) can increase INR (rarely beyond 1.3). Discuss with a senior clinician if there is any uncertainty
  • The admitting doctor should consider if referral to liaison psychiatry is appropriate


Published: 29/01/2021. Links updated 23/02/22. Medicines Update blogs are correct at time of publication